This invention relates to improved methods and apparatus for generating a linear vibratory output force (also sometimes called a reciprocating output force) having a controllable amplitude.
A pair of eccentric masses rotating in opposite directions about a common axis in respective closely spaced parallel planes, or rotating in opposite directions about respective parallel axes in a common plane, cooperate to produce an approximately linear vibratory force, assuming (1) that the rotating force vectors of the individual masses have the same amplitude, (2) that both masses rotate at the same speed, and (3) that the masses are properly phased relative to one another. The vibratory output force acts along a line that is parallel to the plane or planes in which the eccentric masses rotate. This line is also perpendicular to a line between the centers of gravity of the two masses when the two masses are at phase angles that differ by 180.degree..
Two pairs of masses, each pair counter-rotating as described above, can be operated together with their vibratory output forces aligned. Assuming that all four masses rotate at the same speed, the phase relationship between the two pairs influences the extent to which the output forces of the two pairs add to or subtract from one another. Thus the phase relationship between the two pairs controls the amplitude of the net vibratory output force (the vector sum of the vibratory output forces of the two pairs).
There are applications of vibratory force generators in which it is desirable to be able to control amplitude substantially independently of frequency and phase. For example, vibratory force generators may be used to counteract the effect of helicopter rotor blades passing over the fuselage of the helicopter. In general, the frequency and phase of the vibratory force generator output must be matched to rotor speed and angular position. At any given rotor speed, however, the angle of attack of the rotor blades may vary, and this will change the amplitude of the vibratory force generator output that is required to counteract the effect of the rotor blades on the fuselage. Hence the requirement to be able to change vibratory force generator output amplitude substantially independent of frequency and phase.
Austin et al. U.S. Pat. No. 3,208,292 shows a system of four rotating masses in two pairs of two counter-rotating masses powered by a single motor with phase adjustment between the pairs. However, the Austin et al. patent does not disclose or suggest a system which is capable of high-speed, dynamic variation of such vibratory output force parameters as frequency, phase, and amplitude. Nor does the Austin et al. patent disclose or suggest a system which is adapted to produce amplitude variation substantially independently of frequency and phase.
Jensen U.S. Pat. No. 5,005,439 shows a system in which each of four rotating eccentric masses is powered by a separate motor. Assuming separate control of the motors, the Jensen system can produce a wide range of output parameter combinations. But four separate motors may undesirably increase the cost, size, weight, complexity, etc., of the system.
In view of the foregoing, it is an object of this invention to provide improved and simplified linear vibratory force generator apparatus and methods.
It is a more particular object of this invention to provide relatively simple linear vibratory force generator apparatus and methods which can perform such functions as varying the amplitude of the output force substantially independently of the frequency and phase of that force.